This application claims priority of Taiwanese Application No. 091208831, filed on Jun. 13, 2002.
1. Field of the Invention
This invention relates to a rotary woodworking machine, more particularly to a rotary woodworking machine with a speed ratio varying device for a transmitting shaft which is driven by an output shaft of a motor.
2. Description of the Related Art
A conventional rotary woodworking machine, such as one having a sand-belt and pulley assembly, an emery wheel, or a sanding drum, generally includes a gear box in which a plurality of different gears are operably coupled to a motor and a transmitting shaft for varying the rotational speed of an output end of the transmitting shaft. However, since the rotational speed of the transmitting shaft depends on the coupling of the different gears, it cannot be freely varied. Moreover, the noise generated during gear change is loud, and the gear box is bulky, which are disadvantageous.
The object of the present invention is to provide a rotary woodworking machine which has a noiseless speed ratio varying device for a transmitting shaft and which permits the transmitting shaft to rotate at a desired speed.
According to this invention, the rotary woodworking machine includes a machine frame with first and second walls opposite to each other in a longitudinal direction. A motor has an output shaft extending along and rotatable about a first axis parallel to the longitudinal direction to deliver a drive force. The output shaft has a coupling end disposed between the first and second walls. A transmitting shaft extends along and is rotatable about a second axis parallel to the first axis, and has first and second ends which extend outwardly of the first and second walls, respectively, and a middle portion between the first and second ends. First and second rotary woodworking members are coupled to and are rotatable with the first and second ends of the transmitting shaft, respectively.
A speed ratio varying device includes first and second pulleys, a control unit, and a belt. The first pulley has a first fixed disc which is mounted securely on the middle portion, and a first movable disc which is splined to the middle portion to be movable relative to the first fixed disc along the second axis. The first fixed and movable discs respectively have first belt-engaging surfaces which cooperatively define therebetween a first belt receiving space. The control unit is mounted on the machine frame, and has an operable member which is turnable to move the first movable disc along the second axis toward or away from the first fixed disc. The second pulley has a second fixed disc which is mounted securely on the coupling end, and a second movable disc which is splined to the coupling end to be movable relative to the second fixed disc along the first axis. The second fixed and movable discs respectively have second belt-engaging surfaces which cooperatively define therebetween a second belt receiving space. A biasing member is disposed to bias the second movable disc toward the second fixed disc. The belt is trained on the first and second pulleys, and is frictionally slidable on the first and second belt-engaging surfaces. The belt has a first lengthwise end which cooperates with the middle portion to define a first radial distance therebetween, and a second lengthwise end which is opposite to the first lengthwise end in a direction transverse to the longitudinal direction and which cooperates with the coupling end to define a second radial distance therebetween. Turning of the operable member results in movement of the first movable disc along the second axis between first and second positions. In the first position, the first movable disc is closer to the first fixed disc so that the first lengthwise end is remote from the middle portion so as to result in a greater length of the first radial distance, and the second movable disc is kept apart from the second fixed disc by a tension force which is generated as a result of displacement of the second lengthwise end toward the coupling end of the output shaft and which acts against biasing action of the biasing member. In the second position, the first movable disc is remote from the first fixed disc so that the first lengthwise end is proximate to the middle portion so as to result in a smaller length of the first radial distance, and the second movable disc is held close to the second fixed disc by the biasing action of the biasing member.